CODEWITHSUNDEEP
javaregex
user4786688
user4786688

Reputation:

Escaping $ with \$

I need to escape the $ and therefore I need to replace all occurrences of $ with \$

So I wrote this method:

// String#replaceAll(String regex, String replacement)
public String escape$(String str) {
    // the first \\$ to escape it in regular expression
    // the second is a normal String so \\$ should mean \$
    return str.replaceAll("\\$", "\\$");
}


String s = "$some$$text here";
System.out.println(escape$(s));

Before I submitted for production use, I thought hmmm let's test that even though I was certain it should work. And so I did...

Well you guessed it. It doesn't work! It returns the same thing!

// expected result of the above: \$some\$\$text here
// reality: $some$$text here

So why doesn't this work?!

Upvotes: 0

Views: 143

Answers (2)

user557597
user557597

Reputation:

For Java regex, it's not just that you have to double escape a string for the language,
which always has to be done.

It's that you have to escape the dollar sign for the engine as well to
distinguish it from a capture variable.

The replace string is actually a template for a string formatter.

Always write the replacement text in it's raw form first.
The raw form is what is presented to the engine as a template for the formatter.

Raw: \\ + \$ <- the engine parses this as \ + $ (two separate literals)

Combined Raw: \\\$

Finally, for the language, just escape the escapes.

Stringed: "\\\\\\$"

Upvotes: 0

Mena
Mena

Reputation: 48404

You need to double-escape the replacement.

You probably don't want to use replaceAll, as you'd actually need to double-double escape it, but you're not using regular expressions here.

Instead, you can just use replace, which takes literals (and uses replaceAll in the background, with quoted values - see Matcher#quoteReplacement).

Here are two examples:

System.out.println("$".replaceAll("\\$", "\\\\\\$"));
System.out.println("$".replace("$", "\\$"));

Output

\$
\$

Upvotes: 4

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